As a percutaneous absorption preparation for the administration of a drug to a living body through the skin surface, various external preparations used by being patched to the skin surface such as cataplasm or medical tape have been developed. Among such preparations, a medical tape having a drug, which exhibits systemic pharmacological effects, contained therein has particularly attracted attentions. Under such situations, tape-shaped percutaneous absorption preparations each having a pharmacologically active substance, such as nitroglycerin, isosorbide nitrate, steroid preparation, non-steroid preparation, anesthesia or antihypertensive drug, incorporated in a pressure-sensitive adhesive has been proposed and developed. Some of them have already been put on the market.
Such percutaneous absorption preparations are each prepared by incorporating a percutaneously absorptive drug in an acrylic or synthetic rubber series pressure-sensitive adhesive. Only by the application of it to the skin, the drug is absorbed continuously in a living body and then exhibits excellent pharmacological action.
Since they have a percutaneously absorptive drug incorporated in a pressure-sensitive adhesive, however, a decomposition product appears as a result of the interaction between various trace components in the pressure-sensitive adhesive and the drug, whereby the resulting percutaneous absorption preparation is colored. In addition, the colored degree of many preparations tends to be heightened during the storage of the preparation.
In general, the reaction of a drug with the component in a pressure-sensitive adhesive produces a decomposition product so that it is the common practice to reveal the structure of the decomposition product and then add a decomposition inhibitor (antioxidant, stabilizer or the like) to prevent the decomposition. With regards to the coloration phenomenon, most of the reaction products of a trace component cause so much coloring as to exceed the permissible limit of the appearance of the preparation and it is considerably difficult to investigate means for preventing such coloring.
As a matter of fact, therefore, it is generally inevitable to depend on time-spending and inefficient means for screening a proper compound, more specifically, to add a large number of compounds to a preparation respectively and select a proper compound which does not cause coloring of the preparation.